Re: very slow queries and ineffective vacuum

On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <
lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
>
> Perhaps I'm missing some indexes on the tables (creating them on the
> columns on which the where clause was used in the long queries seemed to
> halve their times). Also how can I monitor my transactions and if they are
> closed properly?
>

To track transactions that have not been left idle but not committed or
rolled back you would:

1) Set track_activities true in the config (doc:
http://www.postgresql.org/docs/current/static/runtime-config-statistics.html#GUC-TRACK-ACTIVITIES
)
2) Query the pg_stat_activity view for connections where state = 'idle in
transaction' (doc:
http://www.postgresql.org/docs/current/static/monitoring-stats.html#PG-STAT-ACTIVITY-VIEW
)

As you would suspect, transactions that have been left "idle in
transaction" prevent vacuum from removing old tuples (because they are
still in scope for that transaction)

*Will J. Dunn*
*willjdunn.com <http://willjdunn.com>*

On Tue, Jun 30, 2015 at 4:27 PM, William Dunn <dunnwjr(at)gmail(dot)com> wrote:

> Hello Lukasz,
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <
> lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
>>
>> There doesn't seem to be any issues with disk space, memory or CPU, as
>> neither of those is even 50% used (as per df and top).
>>
>
> Are you using the default PostgreSQL configuration settings, or have you
> custom tuned them? The default settings are targeted for wide compatibility
> and are not optimized for performance. If PostgreSQL is performing badly
> and using a small amount of system resources it is likely some tuning is
> needed. See docs:
> http://www.postgresql.org/docs/current/static/runtime-config.html
>
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <
> lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
>>
>> For whatever reason there is also no data in pg_stat* tables.
>>
>
> You can also turn on tracking (for statistics views) by enabling
> statistics collection in the config
> http://www.postgresql.org/docs/current/static/runtime-config-statistics.html
>
> *Will J. Dunn*
> *willjdunn.com <http://willjdunn.com>*
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <
> lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
>> Hello.
>>
>> I have multiple problems with my database, the biggest of which is how to
>> find out what is actually wrong.
>>
>> First of all I have a 9.3 postgres database that is running for about a
>> month. Right now the queries on that database are running very slowly
>> (select with a simple "where" on a non-indexed column on a table with about
>> 5000 records takes 1,5s, a complicated hibernate select with 7 joins on
>> tables of about 5000 records takes about 15s, insert or update on a table
>> with 35000 records takes up to 20 mins).
>>
>> The tables and indexes on those tables are bloated to the point where
>> this query: https://wiki.postgresql.org/wiki/Show_database_bloat shows
>> wasted bytes in hundreds of MB.
>>
>> For whatever reason there is also no data in pg_stat* tables.
>>
>> So due to the long query times, there are multiple errors in my
>> application logs like "No free connection available" or "Could not
>> synchronize database state with session", or "Failed to rollback
>> transaction" and the application fails to start in the required time.
>>
>> The only thing that helps fix the situation seems to be vacuum full of
>> the entire database. Regular vacuum doesn't even lower the dead tuples
>> count (which appear by the thousands during application launching). Reindex
>> of all the indexes in the database didn't help as well. All autovacuum
>> parameters are default.
>>
>> There doesn't seem to be any issues with disk space, memory or CPU, as
>> neither of those is even 50% used (as per df and top).
>>
>> Is there any good tool that will monitor the queries and generate a
>> report with useful information on what might be the problem? I tried
>> pg_badger, but all I got were specific queries and their times, but the
>> long query times are just one of the symptoms of what's wrong with the
>> database, not the cause.
>>
>> Perhaps I'm missing some indexes on the tables (creating them on the
>> columns on which the where clause was used in the long queries seemed to
>> halve their times). Also how can I monitor my transactions and if they are
>> closed properly?
>>
>> I will be grateful for any help and if you need more details I can
>> provide them if possible.
>>
>> Best regards.
>> Lukasz
>>
>
>